The purpose of this investigation is to define the molecular nature of the murine cell surface components Thy-1, H-2 and GIX (gp70). Thy-1 and GIX are expressed on T-lymphocytes and are indicative of their state of differentiation. GIX is also related to MuLV glycoproteins and expressed on thymus derived leukemias. These components will be obtained from murine lymphoblastoid cell lines grown in 70 and 200 liter culture vessels. Plasma membranes from the cell lines will be purified and the components solubilized with detergents. The solubilized Thy-1, H-2 and GIX will then be purified by a combination of techniques including lectin affinity chromatography, gel filtration, ion exchange chromatography and isoelectric focusing. These procedures have been utilized to great advantage in the isolation of murine Thy-1.1 and Thy-1.2. The purified components will be physicochemically characterized by determining their molecular weight, amino acid and carbohydrate compositions and the existence of subunits. Thy-1 has been isolated in quantities sufficient to allow limited structural analysis of the sequence of amino acids. Providing H-2 and GIX can be isolated in sufficient quantities these molecules will also be analyzed in a limited degree with regard to their primary structure. From these studies one should be able to make deductions regarding the differences in specificities expressed on leukemic cells as opposed to normal ones. It is anticipated that knowledge concerning the molecular nature of cell surface components will have significance in clarifying the normal differentiation process as well as the nature of cancer. Moreover, structural data on these molecules should aid in a better understanding of the molecular nature of lymphocyte membrane components.